Method and apparatus for collecting bacterial cells, method for acclimatizing bacterial cells, and wastewater treatment equipment

ABSTRACT

A method for collecting bacterial cells includes feeding water to be treated containing ammonium and nitrite to an anaerobic ammonium oxidation vessel to denitrify ammonium and nitrite by anaerobic ammonium oxidizing bacteria for forming denitrified treated water, feeding the denitrified treated water to a precipitation vessel or membrane separation unit to collect anaerobic ammonium oxidizing bacteria in the denitrified treated water in a separated sludge obtained by solid-liquid separation in the precipitation vessel or membrane separation in the membrane separation unit, and optionally returning the denitrified treated water from the precipitation vessel or membrane separation unit to the anaerobic ammonium oxidation vessel.

This is a Divisional application of U.S. patent application Ser. No.11/126,231 filed May 11, 2005. The entire disclosure of the priorapplication is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus forcollecting bacterial cells, a method for acclimatizing bacterial cells,and wastewater treatment equipment, in particular, to a technique forcollecting anaerobic ammonium oxidizing bacteria used for anaerobicammonium oxidation and a technique for acclimatizing collected anaerobicammonium oxidizing bacteria.

2. Description of the Related Art

Nitrogen components contained in sewage and industrial effluent causeeutrophication in lakes and lower the level of dissolved oxygen inrivers, and thus must be removed. Examples of main nitrogen componentscontained in sewage and industrial effluent include ammonium nitrogen,nitrite nitrogen, nitrate nitrogen, and organic nitrogen.

Conventionally, when nitrogen in such wastewater has a lowconcentration, ion exchange and oxidation by chlorine or ozone are usedto remove nitrogen. When the nitrogen has a medium or highconcentration, biological treatment is employed and usually operated inthe following conditions.

In the biological treatment, nitrification and denitrification treatmentare performed by aerobic nitrification and anaerobic denitrification. Inthe aerobic nitrification, ammonium nitrogen and nitrite nitrogen areoxidized by ammonium oxidizing bacteria (Nitrosomonas, Nitrosococcus,Nitrosospira, Nitrosolobus, etc.), and nitrite oxidizing bacteria(Nitrobactor, Nitrospina, Nitrococcus, Nitrospira, etc). On the otherhand, in the anaerobic denitrification, denitrification is performed byheterotrophic bacteria (Pseudomonas denitrificans, etc.).

A nitrification vessel for aerobic nitrification is operated under aload of 0.2 to 0.3 kg-N/m³/day, and a denitrification vessel foranaerobic denitrification is operated under a load of 0.2 to 0.4kg-N/m³/day. To treat nitrogen contained in a total concentration of 30to 40 mg/L in sewage, the sewage must be retained in a nitrificationvessel for 6 to 8 hours and in a denitrification vessel for 5 to 8hours, and large-scale treatment vessels are required. Further, anitrification vessel and a denitrification vessel are designed to beoperated under the loads as described above for industrial effluentcontaining only inorganic substances. However, denitrification of suchwastewater requires organic substances, and thus methanol is added at aconcentration three to four times of that of nitrogen. For this reason,not only an initial cost but also a large running cost are required.

In this situation, recently, a method for removing nitrogen comprisinganaerobic ammonium oxidation has been attracted attention (for example,Japanese Patent Application Publication No. 2001-37467 and JapanesePatent Application Publication No. 2003-24990). This anaerobic ammoniumoxidation is a method comprising simultaneously denitrifying ammonium asa hydrogen donor and nitrite as a hydrogen receptor by anaerobicammonium oxidizing bacteria according to the following reaction formula:

1.0NH₄+1.32NO₂+0.066HCO₃+0.13H⁺→1.02N₂+0.26NO₃+0.066CH₂O_(0.5)N_(0.15)+2.03H₂O  (FormulaI)

This method has advantages in that ammonium used as a hydrogen donor canconsiderably reduce the amount of methanol used for denitrification andreduce the amount of a sludge produced, etc. Thus, the method isconsidered to be an effective method for removing nitrogen in thefuture.

SUMMARY OF THE INVENTION

However, it is difficult and takes a very long time to attach anaerobicammonium oxidizing bacteria used for the anaerobic ammonium oxidation topellets and acclimatize the bacteria (cause the bacteria toproliferate), which is a great obstacle to practical application of themethod.

It is reported that the bacteria carrying out anaerobic ammoniumoxidation are Planctomycete, although the details are not clear, and thebacteria have a very low proliferation rate of 0.001 h⁻¹ (Strous, M. etal., Nature, 400, 446 (1999)).

According to Japanese Patent Application Publication No. 2003-24990, thebacteria have a very small specific proliferation rate of 0.02 to 0.05days⁻¹, and it takes 14 to 35 culture days to double the amount of thebacterial cells.

To immobilize anaerobic ammonium oxidizing bacteria on pellets, it isnecessary to attach the bacteria to an immobilizing material and causethe bacteria to proliferate first. However, since the proliferation rateis small as described above, even this attachment stage takes a longtime.

Actual production equipment of a nitrogen removal system utilizinganaerobic ammonium oxidation has not been operated in Japan so far.Accordingly, when actual production is started, due to an activatedsludge or the like, it is necessary to start production after a longacclimatization period required, or to provide a culturing plantmanufactured by a plant manufacturer, etc. for culturing anaerobicammonium oxidizing bacteria.

Because of the above circumstances, when starting operation of awastewater treatment system utilizing anaerobic ammonium oxidizingbacteria, the system requires a long acclimatization period that has notbeen underwent in acclimatization of conventional wastewater treatment.

In the system to be practically used, not only is a huge plant is to beprovided, which requires expensive equipment and operation managementcosts for operation, but also a large amount of nitrogen wastewater mustbe controlled.

The present invention has been achieved in view of such circumstances.An object of the present invention is to provide a method and anapparatus for collecting bacterial cells, a method for acclimatizingbacterial cells, and wastewater treatment equipment which canefficiently collect highly active anaerobic ammonium oxidizing bacteriafrom water treated in an anaerobic ammonium oxidation vessel, can carryout acclimatization in a short time by utilizing the collected anaerobicammonium oxidizing bacteria, and thus can not only solve the aboveproblems but also improve performance of anaerobic ammonium oxidation.

According to a first aspect of the present invention, to attain theaforementioned object, there is provided a method for collectingbacterial cells comprising the steps of: feeding water to be treatedcontaining ammonium and nitrite to an anaerobic ammonium oxidationvessel to denitrify ammonium and nitrite by anaerobic ammonium oxidizingbacteria; and feeding the denitrified treated water to anacclimatization vessel or returning the water through theacclimatization vessel to the anaerobic ammonium oxidation vessel tocollect anaerobic ammonium oxidizing bacteria in the treated water asimmobilized microorganisms attached to an immobilizing material in theacclimatization vessel.

As a result of extensive studies, the inventors of the presentapplication have confirmed that anaerobic ammonium oxidizing bacteriaexist in treated water obtained by treating water to be treatedcontaining ammonium and nitrite by anaerobic ammonium oxidation,although the amount is as small as several mg/L, and the bacteria arehighly active.

Accordingly, by feeding the treated water to an acclimatization vesselwith an immobilizing material or returning the water through theacclimatization vessel to an anaerobic ammonium oxidation vessel,anaerobic ammonium oxidizing bacteria in the treated water can becollected as immobilized microorganisms attached to the immobilizingmaterial in the acclimatization vessel. By acclimatizing the collectedimmobilized microorganisms, the time for acclimatizing anaerobicammonium oxidizing bacteria can be considerably reduced as compared withthe prior art.

According to the present invention, since anaerobic ammonium oxidizingbacteria can be acclimatized in a short time, anaerobic ammoniumoxidation can exhibit improved performance, and the apparatus does notneed to have a large size.

According to a second aspect of the present invention, there is providedthe method for collecting bacterial cells according to the first aspect,wherein the immobilizing material for immobilized microorganisms is oneof pellets and an immobilized bed. Any pellets or immobilized bed may beused as the immobilizing material for immobilized microorganisms. Whenimmobilized microorganisms are introduced into or placed in an anaerobicammonium oxidation vessel in which acclimatization is to be started,anaerobic ammonium oxidizing bacteria can be prevented from being flownout from the anaerobic ammonium oxidation vessel, and acclimatization inthe anaerobic ammonium oxidation vessel can be carried out in a furthershorter period.

According to a third aspect of the present invention, to attain theaforementioned object, there is provided a method for collectingbacterial cells comprising the steps of: feeding water to be treatedcontaining ammonium and nitrite to an anaerobic ammonium oxidationvessel to denitrify ammonium and nitrite by anaerobic ammonium oxidizingbacteria; and feeding the denitrified treated water to a precipitationvessel or membrane separation unit or returning the water through theprecipitation vessel or membrane separation unit to the anaerobicammonium oxidation vessel to collect anaerobic ammonium oxidizingbacteria in the treated water in a separated sludge obtained bysolid-liquid separation in the precipitation vessel or membraneseparation in the membrane separation unit.

In the above first aspect, anaerobic ammonium oxidizing bacteria arecollected as immobilized microorganisms attached to an immobilizingmaterial. In contrast, in the third aspect, a sludge of bacterial cells,specifically, bacterial cells themselves of anaerobic ammonium oxidizingbacteria are collected. The collected sludge of bacterial cells may beintroduced as is into an anaerobic ammonium oxidation vessel in whichacclimatization is to be carried out, or may be directly attached to animmobilizing material and introduced into an anaerobic ammoniumoxidation vessel in which acclimatization is to be started. In thiscase, the immobilizing material is not limited to an immobilizingmaterial to which the sludge of bacterial cells is attached such aspellets or immobilized bed. Entrapping immobilization pellets in whichthe sludge of bacterial cells is entrapped and immobilized in a gel maybe used as the immobilizing material.

According to a fourth aspect of the present invention, there is providedthe method for collecting bacterial cells according to the third aspect,wherein the membrane separation unit is a rotary flat membrane unit.This is because, although a membrane such as a rotary flat membrane,immersion membrane, or hollow fiber membrane may be used in the membraneseparation unit, it is preferable to use a rotary flat membrane tomaintain the life of the membrane for a long time.

According to a fifth aspect of the present invention, to attain theaforementioned object, there is provided a method for collectingbacterial cells comprising the steps of: feeding water to be treatedcontaining ammonium and nitrite to an anaerobic ammonium oxidationvessel to denitrify ammonium and nitrite by anaerobic ammonium oxidizingbacteria; and feeding the denitrified treated water to a precipitationvessel, in which an acclimatization container is stored, to causeanaerobic ammonium oxidizing bacteria in the treated water to beattached to an immobilizing material in the acclimatization container,so that the anaerobic ammonium oxidizing bacteria are collected, and, atthe same time, to collect anaerobic ammonium oxidizing bacteria in aseparated sludge obtained by solid-liquid separation in theprecipitation vessel.

According to the fifth aspect, not only anaerobic ammonium oxidizingbacteria as immobilized microorganisms but also bacterial cellsthemselves of anaerobic ammonium oxidizing bacteria can be collected.Specifically, among anaerobic ammonium oxidizing bacterias in treatedwater anaerobic ammonium oxidizing bacteria floating in the treatedwater are attached to the immobilizing material and collected, andanaerobic ammonium oxidizing bacteria in a sludge flown out in companywith the treated water are precipitated and collected as a sludge ofbacterial cells. Thus, all anaerobic ammonium oxidizing bacteria in thetreated water can be efficiently collected.

According to a sixth aspect of the present invention, to attain theaforementioned object, there is provided an apparatus for collectingbacterial cells, which is configured to carry out the method forcollecting bacterial cells according to any one of the first to fifthaspects.

The apparatus has a configuration for applying the method for collectingbacterial cells of the present invention, and thus can efficientlycollect highly active anaerobic ammonium oxidizing bacteria remaining inwater treated by anaerobic ammonium oxidation. Therefore, theacclimatization period can be considerably reduced when the collectedanaerobic ammonium oxidizing bacteria are used for acclimatization asinoculum.

According to a seventh aspect of the present invention, to attain theaforementioned object, there is provided a method for acclimatizinganaerobic ammonium oxidizing bacteria, comprising the step ofacclimatizing anaerobic ammonium oxidizing bacteria as inoculumcollected by the method for collecting bacterial cells according to anyone of the first to fifth aspects in an acclimatization vessel or ananaerobic ammonium oxidation vessel to be started up.

In this case, the acclimatization period can be reduced by returninganaerobic ammonium oxidizing bacteria collected by the present inventionfrom treated water of an anaerobic ammonium oxidation vessel in whichacclimatization is in progress to the anaerobic ammonium oxidationvessel in which acclimatization is in progress. Alternatively, theacclimatization period can be reduced by using anaerobic ammoniumoxidizing bacteria collected from treated water of an anaerobic ammoniumoxidation vessel in which acclimatization is completed as inoculum foranother anaerobic ammonium oxidation vessel in which acclimatization isto be started or an acclimatization vessel separately prepared.

According to an eighth aspect of the present invention, to attain theaforementioned object, there is provided equipment for treatingwastewater by anaerobic ammonium oxidation, the wastewater treatmentequipment comprising the apparatus for collecting bacterial cellsaccording to the sixth aspect.

With the apparatus for collecting bacterial cells of the presentinvention provided as a part of equipment for treating wastewater byanaerobic ammonium oxidation, highly active anaerobic ammonium oxidizingbacteria in treated water can be efficiently collected. By starting upan anaerobic ammonium oxidation vessel utilizing the collected anaerobicammonium oxidizing bacteria, the acclimatization period can beconsiderably reduced.

As described above, the method and the apparatus for collectingbacterial cells of the present invention can efficiently collect highlyactive anaerobic ammonium oxidizing bacteria from water treated in ananaerobic ammonium oxidation vessel.

In addition, the method for acclimatizing anaerobic ammonium oxidizingbacteria of the present invention comprises carrying out acclimatizationusing, as inoculum, anaerobic ammonium oxidizing bacteria collected bythe method for collecting bacterial cells of the present invention, andtherefore can reduce the acclimatization period considerably, solve theproblems of the prior art, and improve performance of anaerobic ammoniumoxidation.

Further, the wastewater treatment equipment comprising the apparatus forcollecting bacterial cells of the present invention as a part of theconfiguration can efficiently collect highly active anaerobic ammoniumoxidizing bacteria in treated water. By starting up an anaerobicammonium oxidation vessel utilizing the collected anaerobic ammoniumoxidizing bacteria, the acclimatization period can be considerablyreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view for describing the entire configuration ofwastewater treatment equipment by anaerobic oxidation, comprising theapparatus for collecting bacterial cells according to a first embodimentof the present invention;

FIG. 2 is a conceptual view for describing the entire configuration ofwastewater treatment equipment by anaerobic ammonium oxidation,comprising the apparatus for collecting bacterial cells according to asecond embodiment of the present invention;

FIG. 3 is a conceptual view for describing the entire configuration ofwastewater treatment equipment, which shows a modification of the firstembodiment;

FIG. 4 is a conceptual view for describing the entire configuration ofwastewater treatment equipment by anaerobic ammonium oxidation,comprising the apparatus for collecting bacterial cells according to athird embodiment of the present invention; and

FIG. 5 is a conceptual view for describing the entire configuration ofwastewater treatment equipment, which shows a modification of the thirdembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the method and the apparatus for collectingbacterial cells, the method for acclimatizing bacterial cells, and thewastewater treatment equipment of the present invention will bedescribed below by way of the accompanying drawings.

FIG. 1 is a conceptual view for describing the entire configuration ofwastewater treatment equipment 10 by anaerobic ammonium oxidation,comprising the apparatus for collecting bacterial cells according to afirst embodiment of the present invention.

As shown in FIG. 1, the wastewater treatment equipment 10 is configuredby providing, as a main constituent, an acclimatization vessel 14 forcollecting and acclimatizing anaerobic ammonium oxidizing bacteriadownstream to an anaerobic ammonium oxidation vessel 12. Here, theapparatus for collecting bacterial cells consists of the acclimatizationvessel 14.

Water to be treated containing ammonium and nitrite flowing in a rawwater pipe 20 is fed to the anaerobic ammonium oxidation vessel 12 by apump (not shown). The water treated in the anaerobic ammonium oxidationvessel 12 is fed through a first pipe 22 to the acclimatization vessel14, and is discharged from the acclimatization vessel 14 through atreated water pipe 24 to outside the system.

Water to be treated (raw water) containing ammonium and nitrite is flowninto the anaerobic ammonium oxidation vessel 12, and ammonium andnitrite contained in the raw water are simultaneously denitrified byanaerobic ammonium oxidizing bacteria in the anaerobic ammoniumoxidation vessel 12.

The acclimatization vessel 14 includes one of pellets and an immobilizedbed as an immobilizing material. When the treated water is brought intocontact with the immobilizing material, anaerobic ammonium oxidizingbacteria in the treated water are attached to the immobilizing material.Immobilized microorganisms with anaerobic ammonium oxidizing bacteriaattached to and immobilized on the immobilizing material are thusformed. With the immobilized microorganisms formed, anaerobic ammoniumoxidizing bacteria in the treated water are collected.

The acclimatization vessel 14 is preferably closed, and preferably has astructure into or from which the immobilizing material can be moved. Forexample, it is efficient if the immobilizing material is previously putin a container with a unit structure through which water can permeateand from which the immobilizing material is prevented from flowing out,such as a box made of a wire mesh or plastic mesh, and the container isdipped in or taken from the acclimatization vessel 14. Further, apressure gauge is preferably installed upstream or downstream to theacclimatization vessel 14. This is because operation of the anaerobicammonium oxidation vessel 12 is stopped when the acclimatization vessel14 is blocked, but such a trouble can be prevented if the pressureupstream or downstream to the acclimatization vessel 14 can be detected.The acclimatization vessel 14 does not necessarily have to be configuredas a “vessel”, and may be incorporated in the treated water pipe 22.

As described above, such anaerobic ammonium oxidizing bacteria have avery low proliferation rate. However, by providing the acclimatizationvessel 14 downstream of the anaerobic ammonium oxidation vessel 12 inthis manner, highly active anaerobic ammonium oxidizing bacteria intreated water of the anaerobic ammonium oxidation vessel 12 can becollected as immobilized microorganisms and acclimatized in theacclimatization vessel 14. Further, the collected active anaerobicammonium oxidizing bacteria may be acclimatized in anotheracclimatization vessel, or may be introduced into or placed in ananaerobic ammonium oxidation vessel to be started up, and acclimatized.Thus, the acclimatization period can be considerably reduced as comparedwith acclimatization from a usual activated sludge.

Examples of the material for pellets as an immobilizing materialinclude, but are not specifically limited to, gels of polyvinyl alcohol,alginic acid, and polyethylene glycol; and plastic pellets of cellulose,polyester, polypropylene, and vinyl chloride. Pellets are preferablyformed in the shape of a sphere, a cylinder, a porous material, a cube,a sponge, a honeycomb, or the like.

Further, granules utilizing self-granulation of microbes may be used.

Examples of the material for an immobilized bed as an immobilizingmaterial include, but are not specifically limited to, plastic materialsof polyethylene, polyester, polypropylene, and vinyl chloride; andactive carbon fibers. Examples of the shape of an immobilized bedinclude, but are not specifically limited to, a shape formed into afiber, a chrysanthemum, or a honeycomb. Further, an immobilized bed maybe formed by packing a basket or the like with microbes immobilized onthe above-described pellets or microbes immobilized on the granules.

According to the apparatus for collecting bacterial cells 10 with such aconfiguration, denitrified treated water is fed to the acclimatizationvessel 14, and anaerobic ammonium oxidizing bacteria are attached to andimmobilized on the immobilizing material in the acclimatization vessel14. Since anaerobic ammonium oxidizing bacteria have a small amount butare highly active, the anaerobic ammonium oxidizing bacteria can beattached to the immobilizing material only by dipping the immobilizingmaterial in the treated water in the acclimatization vessel 14. Thus,the time for acclimatizing anaerobic ammonium oxidizing bacteria can beconsiderably reduced as compared with the prior art.

FIG. 2 is a conceptual view for describing the entire configuration ofwastewater treatment equipment 100 by anaerobic ammonium oxidation,comprising the apparatus for collecting bacterial cells according to asecond embodiment of the present invention. Here, the apparatus forcollecting bacterial cells consists of an acclimatization vessel and aprecipitation vessel. The same apparatus or member as in FIG. 1 will bedescribed with the same reference numeral, and repetition of the samedescription is omitted.

The present embodiment differs from the first embodiment in FIG. 1 inthat the embodiment has a configuration in which a precipitation vessel16 is installed downstream of an anaerobic ammonium oxidation vessel 12,and an acclimatization vessel 14 or an acclimatization container isinstalled in the upper part of the precipitation vessel 16. Thus, amonganaerobic ammonium oxidizing bacterias in treated water anaerobicammonium oxidizing bacteria floating in treated water are attached to animmobilizing material in the acclimatization vessel 14 and collected asimmobilized microorganisms as in the first embodiment. Further,anaerobic ammonium oxidizing bacteria in a sludge flown out in companywith the treated water are precipitated and collected as a sludge ofbacterial cells. Therefore, all anaerobic ammonium oxidizing bacteria inthe treated water can be efficiently collected. The sludge of bacterialcells precipitated in the precipitation vessel 16 may be fed through asecond pipe 26 back to the anaerobic ammonium oxidation vessel 12, ormay be discharged through a sludge discharge pipe 32 to outside thesystem. The sludge of bacterial cells discharged to outside the systemmay be introduced into another acclimatization vessel or anotheranaerobic ammonium oxidation vessel 12 to be started up and acclimatizedas inoculum. Alternatively, the sludge may be directly attached to andimmobilized on an immobilizing material, or entrapped and immobilized inan immobilizing material, to form immobilized microorganisms andintroduce the immobilized microorganisms into another acclimatizationvessel or anaerobic ammonium oxidation vessel. If a membrane separationunit (not shown) is used instead of the precipitation vessel 16, theunit can act and exhibit the effect in the same manner.

FIG. 3 shows wastewater treatment equipment 200 showing a modificationof the first embodiment, in which an acclimatization vessel 14 isprovided in a returning line that causes a part or whole of watertreated in an anaerobic ammonium oxidation vessel 12 to flow into theinlet of the anaerobic ammonium oxidation vessel 12 again. The sameapparatus or member as in FIG. 1 will be described with the samereference numeral, and repetition of the same description is omitted.

Specifically, a part or whole of water treated in the anaerobic ammoniumoxidation vessel 12 is fed through a second pipe 26 as a feedback pipeto the acclimatization vessel 14, and second water treated in theacclimatization vessel 14 is returned through a third pipe 30 as afeedback pipe to the anaerobic ammonium oxidation vessel 12. A returningpump 28 is provided in the second pipe 26 as a feedback pipe.

Thus, only by dipping an immobilizing material such as pellets,granules, or an immobilized bed that can immobilize anaerobic ammoniumoxidizing bacteria thereon in returning water (acclimatization vessel14), anaerobic ammonium oxidizing bacteria can be attached to theimmobilizing material. Accordingly, anaerobic ammonium oxidizingbacteria can be efficiently collected, and immobilized microorganisms inwhich anaerobic ammonium oxidizing bacteria are attached to theimmobilizing material in the acclimatization vessel 14 can beefficiently acclimatized. The anaerobic ammonium oxidizing bacteriacollected in the acclimatization vessel 14 may be acclimatized in anacclimatization vessel separately prepared, or may be acclimatized in ananaerobic ammonium oxidation vessel to be started up. Thus, theacclimatization period can be considerably reduced as compared withacclimatization from a usual activated sludge.

FIG. 4 is a conceptual view for describing the entire configuration ofwastewater treatment equipment 300 by anaerobic ammonium oxidation,comprising the apparatus for collecting bacterial cells according to athird embodiment of the present invention. The same apparatus or memberas in FIG. 1 will be described with the same reference numeral, andrepetition of the same description is omitted. Here, the apparatus forcollecting bacterial cells consists of a rotary flat membrane unit.

The present embodiment differs from the first embodiment in FIG. 1 inthat water to be treated containing ammonium and nitrite is denitrifiedin an anaerobic ammonium oxidation vessel 12, and the treated water ismembrane separated using a rotary flat membrane separation unit 18 toacquire and collect anaerobic ammonium oxidizing bacteria on themembrane surface, together with a sludge flown out from the anaerobicammonium oxidation vessel 12 in company with the treated water.

Specifically, water treated in the anaerobic ammonium oxidation vessel12 is fed through a first pipe 22 to the rotary flat membrane separationunit 18 and membrane separated. The treated water from which a sludge isremoved by membrane separation is discharged through a treated waterpipe 24 to outside the system, and the concentrated solution of whichthe sludge concentration increases due to the membrane separation isreturned through a second pipe 26 as a feedback pipe to the anaerobicammonium oxidation vessel 12.

The rotary flat membrane separation unit 18 is to collect bacterialcells washed out from treated water, and can collect a small amount ofanaerobic ammonium oxidizing bacteria in treated water or returningwater. A sludge of bacterial cells containing anaerobic ammoniumoxidizing bacteria, acquired and collected on the membrane surface ofthe membrane separation unit 18, can be introduced into an anaerobicammonium oxidation vessel to be started up. By collecting a sludgeitself of bacterial cells containing anaerobic ammonium oxidizingbacteria in this manner, not only microbes immobilized by attachment,but also entrapping immobilization pellets in which the sludge ofbacterial cells is entrapped and immobilized in a gel can be formed.

Examples of the membrane separation device include, in addition to therotary flat membrane separation unit 18, a membrane separation unitusing an immersion membrane or a hollow fiber membrane. In this membraneseparation device, the membrane surface must not be washed by aeration.This is because the collected anaerobic ammonium oxidizing bacteria arekilled by washing by aeration. Of a rotary flat membrane, an immersionmembrane, and a hollow fiber membrane, a rotary flat membrane ispreferably used to maintain the membrane life for a long time.

The membrane separation device may be used for feeding back the sludgecollected by membrane separation, when laboratory equipment is startedup.

FIG. 5 is a conceptual view for describing the entire configuration ofwastewater treatment equipment 400, which shows a modification of FIG.4. The same apparatus or member as in FIGS. 1 and 4 will be describedwith the same reference numeral, and repetition of the same descriptionis omitted.

The present embodiment differs from the fourth embodiment in FIG. 4 inthat the equipment is configured so that a rotary flat membraneseparation unit 18 can discharge a sludge of bacterial cells ofanaerobic ammonium oxidizing bacteria acquired and collected on themembrane surface to outside the system or feed back the sludge to ananaerobic ammonium oxidation vessel 12.

Specifically, water treated in the anaerobic ammonium oxidation vessel12 diverges, and a part of the water is discharged through a treatedwater pipe 24 to outside the system. The remaining treated water is fedthrough a second pipe 26 as a feedback pipe to the rotary flat membraneseparation unit 18. The concentrated solution with a high sludgeconcentration separated in the membrane separation unit 18 is returnedthrough a fourth pipe 34 as a feedback pipe to the anaerobic ammoniumoxidation vessel 12. A part of the sludge of bacterial cells containinganaerobic ammonium oxidizing bacteria acquired and collected on themembrane surface in the membrane separation unit 18 can be returnedthrough a fifth pipe 36 as a sludge feedback pipe to the anaerobicammonium oxidation vessel 12, or can be discharged through a sludgedischarge pipe 32 to outside the system. The sludge discharged tooutside the system may be introduced into an anaerobic ammoniumoxidation vessel to be started up, or may be used for formingimmobilized microorganisms in which the sludge of bacterial cells areattached to and immobilized on an immobilizing material or immobilizedmicroorganisms in which the sludge of bacterial cells is entrapped andimmobilized in a gel.

EXAMPLES

Examples of the present invention will be described below. However, thepresent invention should not be limited to these examples.

Example 1

A test of acclimatization of anaerobic ammonium oxidizing bacteria wascarried out using wastewater treatment equipment 10 of anaerobicammonium oxidation shown in FIG. 1.

(Wastewater Subjected to Test)

As the wastewater subjected to the test, inorganic synthesizedwastewater was used.

As the raw water composition, a composition shown in Table 1 was usedwith reference to A. A. van de Graaf et al., Microbiology (1996), 142,pp. 2187-2196. Operation was carried out by changing the nitritenitrogen (NO₂—N) concentration and the ammonium nitrogen (NH₄—N)concentration.

TABLE 1 Substrate Amount added NaNO₂ 172-1330 (mg/L) (NH₄)SO₄ 175-1350(mg/L) KHCO₃     500 (mg/L) KH₂ PO₄      27 (mg/L) MgSO₄•7H₂O     300(mg/L) CaCl₂•2H₂O     180 (mg/L) T. Ellement S1      1 (mL/L) T.Ellement S2      1 (mL/L) (Remarks) T. Ellement S1: EDTA: 5 g/L, FeSO₄:5 g/L T. Ellement S2: EDTA: 15 g/L, ZnSO₄•7H₂O: 0.43 g/L, CoCl₂•6H₂O:0.24 g/L, MnCl₂•4H₂O: 0.99 g/L, CuSO₄•5H₂O: 0.25 g/L, NaMoO₄•2H₂O: 0.22g/L, NiCl₂•6H₂O: 0.19 g/L, NaSeO₄•10H₂O: 0.21 g/L, H₃BO₄: 0.014 g/L

(Treatment Conditions)

Operation was carried out at a water temperature of 36° C., at an HRT of3 hours, and at a denitrification rate of 2.8 to 3.2 kg-N/m³/day. The SSconcentration in the treated water at this time was 0.2 to 2.0 mg/L. Anonwoven biomass carrier was put in an acclimatization vessel 14 in FIG.1 as an immobilizing material. After dipping for about 3 weeks, thenonwoven biomass carrier was taken out and subjected to the followingcontinuous flow test.

The wastewater was adjusted to have an NH₄—N concentration of 35 mg/Land an NO₂—N concentration of 35 mg/L with reference to Table 1, andacclimatization was carried out at an HRT of 6 hours to gradually raisethe nitrogen concentration in the raw water. As a result, thedenitrification rate reached 2.8 kg-N/m³/day on the 42nd day afterstarting the operation. Thus, it was confirmed that the acclimatizationwas successful.

Comparative Example 1

A test was carried out under the same operation conditions as in Example1, except for using a completely brand-new nonwoven biomass carrier.

The acclimatization vessel was packed with a brand-new nonwoven biomasscarrier, and a sludge of anaerobic ammonium oxidizing bacteria was addedthereto. As in Example 1 (volume in vessel: 300 mg/L, on a total volumebasis), the wastewater was adjusted to have an NH₄—N concentration of 35mg/L and an NO₂—N concentration of 35 mg/L, and acclimatization wascarried out at an HRT of 6 hours. After 60 days, it was confirmed thatthe acclimatization vessel was finally started up.

It is known that a sludge of anaerobic ammonium oxidizing bacteria canbe turned into a sedimentary floc. Further, since bacterial cells otherthan the bacteria are dispersed and washed out, it is difficult to causethe cells to be attached to a nonwoven biomass carrier in a vessel.

Specifically, the method for collecting bacterial cells of the presentinvention is to form inoculum for the start-up. Not the entire processof acclimatization is carried out by using the inoculum. However, sincethe anaerobic ammonium oxidizing bacteria proliferate only withdifficulty, it is difficult to form inoculum from the bacteria.Therefore, it can be presumed that, by starting up an anaerobic ammoniumoxidation vessel using inoculum formed by the method for collectingbacterial cells of the present invention, the acclimatization period canbe considerably reduced.

Example 2

A test of acclimatization of anaerobic ammonium oxidizing bacteria wascarried out using wastewater treatment equipment 200 of anaerobicammonium oxidation shown in FIG. 3. After dipping methane granules, withwhich an acclimatization vessel 14 was packed, in returning water forabout 10 days, the test was carried out using an UASB (Upflow AnaerobicSludge Blanket) reactor.

An anaerobic ammonium oxidation vessel 12 as a source of returning lines26 and 30 was operated under the same conditions as in Example 1 at awater temperature of 36° C., at an HRT of 3 hours, and at adenitrification rate of 2.8 to 3.2 kg-N/m³/day.

In the same manner as in Example 1, the wastewater was adjusted to havean NH₄—N concentration of 35 mg/L and an NO₂—N concentration of 35 mg/L,and acclimatization was carried out at an HRT of 6 hours to graduallyraise the nitrogen concentration in the raw water. As a result, thedenitrification rate reached 2.1 kg-N/m³/day on the 38th day afterstarting the operation. Thus, it was confirmed that the acclimatizationwas successful.

Example 3

A test of acclimatization of anaerobic ammonium oxidizing bacteria wascarried out using wastewater treatment equipment 300 of anaerobicammonium oxidation shown in FIG. 4.

A sludge of bacterial cells containing anaerobic ammonium oxidizingbacteria acquired and collected on the membrane surface of a rotary flatmembrane separation unit 18 was entrapped and immobilized to obtainentrapping immobilization pellets of anaerobic ammonium oxidizingbacteria. As an immobilizing gel, a polyethylene glycol gel was used.The amount of the bacterial cells immobilized in the pellets was 2.5% ona dry weight basis.

In the same manner as in Example 1, the wastewater was adjusted to havean NH₄—N concentration of 35 mg/L and an NO₂—N concentration of 35 mg/L,and acclimatization was carried out at an HRT of 6 hours to graduallyraise the nitrogen concentration in the raw water. As a result, thedenitrification rate reached 2.6 kg-N/m³/day on the 28th day afterstarting the operation. Thus, it was confirmed that the acclimatizationcan be achieved in a short period.

Example 4

An operation start-up test was carried out using wastewater treatmentequipment 400 of anaerobic ammonium oxidation shown in FIG. 5.

Specifically, acclimatization was carried out in an anaerobic ammoniumoxidation vessel 12 while feeding back all the sludge of bacterial cellscontaining anaerobic ammonium oxidizing bacteria acquired and collectedon the membrane surface of a rotary flat membrane separation unit 18 tothe anaerobic ammonium oxidation vessel 12. A test was also carried outfor a system not comprising the membrane separation unit 18 as acomparative example to conduct a comparative review.

Sponge pellets coated with a polyvinyl alcohol gel were introduced intothe anaerobic ammonium oxidation vessel 12, and the sludge of bacterialcells acquired and collected in the membrane separation unit 18 wasadded, so that the concentration of SS in the vessel 12 was 200 mg/L, tostart operation.

As a result, the time required for confirming that the denitrificationrate reached 1.0 kg-N/m³/day was 38 days in the case of the systemwithout the membrane separation unit 18 (Comparative Example) and 20days in the case of the system with the membrane separation unit 18(Example). Specifically, the present invention could reduce theacclimatization period to about the half.

1. A method for collecting bacterial cells comprising: feeding water tobe treated containing ammonium and nitrite to an anaerobic ammoniumoxidation vessel to denitrify ammonium and nitrite by anaerobic ammoniumoxidizing bacteria for forming denitrified treated water; feeding thedenitrified treated water to a precipitation vessel or membraneseparation unit to collect anaerobic ammonium oxidizing bacteria in thedenitrified treated water in a separated sludge obtained by solid-liquidseparation in the precipitation vessel or membrane separation in themembrane separation unit; and optionally returning the denitrifiedtreated water from the precipitation vessel or membrane separation unitto the anaerobic ammonium oxidation vessel.
 2. The method for collectingbacterial cells according to claim 1, wherein the membrane separationunit is a rotary flat membrane unit.
 3. The method for collectingbacterial cells according to claim 1, the method further comprising:introducing the anaerobic ammonium oxidizing bacteria collected from thedenitrified treated water as inoculum into an acclimatization vessel orinto another anaerobic ammonium oxidation vessel to be started up, andacclimatizing the acclimatization vessel or the another anaerobicammonium oxidation vessel.
 4. The method for collecting bacterial cellsaccording to claim 2, the method further comprising: introducing theanaerobic ammonium oxidizing bacteria collected from the denitrifiedtreated water as inoculum into an acclimatization vessel or into anotheranaerobic ammonium oxidation vessel to be started up, and acclimatizingthe acclimatization vessel or the another anaerobic ammonium oxidationvessel.